The literature is rife with striking examples of the powerful influences of nonvisual stimuli on visual behavior and perception, and with speculations about how such multisensory processes develop. For the most part, hypotheses about the development of multisensory integration have had to rely on inferences and extrapolations from overt behaviors and verbal reports because little was known about the development of its neural basis. Indeed, until recently, little was known about the neural mechanisms of multisensory integration in adults. Recently, however, we have developed a robust neural model of multisensory integration. Using the adult deep layer superior colliculus (SC) neuron, specific principles have been found to govern multisensory integration at the single neuron level and these principles have been shown to be applicable across species and across different areas of the neuraxis as well. Because these principles determine the activity of neurons which constitute a major component of the descending output pathways from the SC (which initiate movements of the eyes, ears and head), they have also proven to be predictive of overt visual attentive and orientation behavior. We propose to study deep layer SC neurons for two interrelated purposes: (1) to understand how they develop the response properties through which they mediate attentive and orientation behaviors, and (2) as a model to understand how the brain develops the capacity to integrate information across sensory modalities. The maturation of these neuronal capabilities is essential for the brain to maximize its processing of information about the external world and to ensure that adaptive responses can be initiated when the individual cues associated with a given event are minimal or ambiguous. Understanding their normal developmental course is an essential step in elaborating strategies to deal with developmental anomalies that compromise attentive mechanisms and the overt behaviors that depend upon them.